1. Field of the Invention
The invention relates to a program-controlled NC data generating method for controlling a CNC wet-grinding machine.
2. Description of Related Art
Although known optical grinding machines allow possibilities for the input of aspherical forms, they offer only very limited possibilities for modification, correction and movement dynamics. Grinding results previously achieved with such machines generally did not satisfy the requirements that exact aspherical forms have to meet. Owing to dimensional deviations of up to 10 μm and inadequate correction possibilities, frequently only by means of a few interpolation points, often to be input manually, effective series production of highly accurate aspheres, in particular aspherical lenses, is rarely possible or not possible at all.
The so-called depression in the center of the workpiece is particularly problematical. The grinding tool or the grinding wheel of a CNC grinding machine, in particular a CNC wet-grinding machine, cannot move away from the center of the asphere infinitely quickly, it is limited in its dynamics. Even an extremely short dwell time of the grinding wheel in the center (even in the range of milliseconds) can cause a hole or a depression at the center of the lens. This problem is also referred to as the center hole effect.
For mathematical reasons, every asphere has the characteristic of steeply rising increasingly toward the edge, i.e. of course also toward the runout region lying outside the useful aspherical region. This on the one hand increases the deformation and, since the grinding/polishing tool also adapts itself to the deformations in a disadvantageous way, is accompanied by great problems, which can have effects extending into the useful region of the asphere. In addition, in the case of concave forms, the useful surface area may be ground into, i.e. destroyed, by the grinding tool.